Motor control system for scanning devices



R. SHER ETAL MOTOR CONTROL SYSTEM FOR SCANNING DEVICES Filed D66. 28, 1945 May 4, 1954 2 Sheets-Sheet l A.C.SOURCE I l l sYNcHRo l I l L Z S R u ORNU lr TEOH O NHSC 2 ESNS fr w HmW. ImPnflbE mf rr F Y N I QH u msm. www NE l- EWE l IODE EIRLv RAVHM DC N n 5mm Y E 3 LVW B RH 2 GMI 8 EH. (MDF. .FMP Smm. 7 M 2 PA 2nVvAMH R GK W O R l/l ET 2 umm Dm ^HAUT mm pms l. D SN G m .Flr E L R Ema WO YIGIA) EIT Awww a snc l ULUA r ASE D'IvG HN WMD PEM A M S ATTORNEY May 4, 1954 R. sHER iss-rm.y

MOTOR CONTROL SYSTEM FOR SCANNING DEVICES` Filed D60. 28, 1945 2 sheets-sheet 2` ATTORNEY Patented May 4, 1954 MOTOR CONTROL SYSTEM FOR SCANNING DEVICES Rudolph Sher, Boston, David B. Nichinson, Brookline, and Clarence W. Schultz, Cambridge, Mass., assignors, by direct and mesne assignments, to the United States of America as represented by the vSecretary of 'the Navy Application December 28, 1945, Serial No. 637,743

10 Claims.

This invention relates to electronic control circuits and more particularly, to those providing electronic control of variable sector scan in a mechanical resonant scanner.

The development of a mechanical resonant scanner (MRS) was the radar systems for an airborne rapid scanning antenna. In such systems, it is generally the practice to tune the antenna inertia with springs so that its natural frequency of oscillation would be that desired for rapid sector scan. If the input energy is not equal to that dissipated in operation the system naturally changes amplitude in a proper direction until equilibrium re sults and stable operation ensues. It is this characteristic which is employed in amplitude control. Therefore, the choice of a driving' motor duty cycle and the quantity of motor energy input selects and controls the amplitude of the scan.

In order to maintain the amplitude of the scanner oscillations for a desired sector scan it is necessary to control within definite limits the duration and timing of the electric motor input pulse. To synchronize the motor input pulse with the angular direction of the scanner, the direction of the motor rotation must be reversed at such time as to allow the motor input pulse to be applied to the scanner in the same direction as the scanner is naturally turning. Considerable diiiiculty has been encountered in maintaining the adjustment and timing of a motor control system mechanically operated at the speed required in a rapid scanner. In accordance with the present invention, and as is explained more fully hereinafter, the electronic control circuit will satisfactorily meet the standards of precision and accuracy required in the synchronization of the motor with a mechanical resonant scanner.

A primary object of the present invention is to provide an electronic control system permitting Variable sector scan in a mechanical resonant scanner (MRS).

Another object of the present invention is to provide means for controlling the duration of the motor pulse applied to a MRS.

A' further object of the present invention is to provide means for controlling the time at which the motor pulse is applied to a MRS.

A still further object of the present invention is to provide means for synchronizing the direction of application of the motor pulse to the natural rotation Yof the MRS.

These and other objects will be apparent from outgrowth of a need in the following specification when taken with the accompanying drawings, in which:

Fig. 1 is a block diagram of an embodiment of the invention; and

Fig. 2 is a phase diagram of certain voltage and current wave forms present in the embodiment represented in Fig. 1. The wave forms are illustrated in relation to the scanner position.

In Fig. 1 the synchro I2 is mounted on the azimuth aXis of the mechanical resonant scanner MRS I3 and is electrically zeroed so that its output voltage is Zero when scanning antenna I3 is in a particular angular position. The stator il of synchro i2 is attached to and rotates with scanner I 3. Two of the stator windings are as schematically illustrated joined by a conductor and are connected to input terminal M. An alternating current of predetermined frequency and comparatively low voltage is applied to the stator coils across terminals I4 and I5. As the stator I! of synchro i 2 rotates with scanner I3 through the scanning sector a variable amplitude alternating voltage is developed in the rotor coil Iii of synchro I2. The instantaneous amplitude of the output voltage from the rotor of synchro I2 is determined by the azimuth angle of scanner i3 relative to the particular zero position previously mentioned. As illustrated in Fig. 2 this output voltage comprises an alternating voltage 39 having an envelope di) of an amplitude proportional to deviation of the azimuth angle of scanner I3 from the midposition, diagrammatically illustrated by the scanner I3 above the waveforms of Fig. 2. Thus, wave form 0 represents the carrier frequency 39 applied to the stator coils of the synchro I 2 at terminals i4 and I5 amplitude modulated at the scanning rate of scanner I3. This amplitude modulated wave form 39, `QE! is fed to a voltage amplifier It having a conventional type, adjustable gain control. The output of voltage ampliiier I5 is illustrated in Fig. 2 by voltage form 4I, similar to Gil but of increased peak amplitude.

Voltage wave form 4I is fed to a diode detector I I which produces a negative unidirectional voltage with respect to ground, and is essentially the negative half of the envelope of wave form 4I, as illustrated in Fig. 2 by voltage Wave form 42. The output of diode detector Il, as represented by Fig. 2 wave form :i2 is applied to the grid of power amplifier I8, the plate load of which is a set of relays I9 which operate normally open switch 2d at the proper time to turn the antenna drive motor 21 on and off. It is desirable to have the motor mechanical driving impulse applied to scanner iii at a point in the cycle thereof just prior to the midposition, and to continue the application of the mechanical force until scanner i3 has just passed through the midposition. Electric motor 2l is normally ener gized until the angle of rotation of scanner i3 reaches a critical value determined by the gain ci" voltage amplier It, at which time the bias on the grid of power ampliiier lil is large enough to reduce the plate current thereof to the point at which relay iii is rie-energized, switch ,2t opens and motor 2l stops.

The broken line shown in Fig. 2 as intersecting wave form d2, represents the critical negative voltage which determines the etective cut oi of power amplifier i3. Wave form [i4 repre'- sents the plate voltage wave form of power am plier i8 in phase relationship to the negative voltage wave form 42 which is applied to the thereof. At point 45 on wave :Ecrin Mi the plato current is suicient to energize relay lil and close switch 2li energizing motor 2l. Motor 2l remains energized until the plate voltage reaches point 4t at which time the plate current is reduced to the point where relay iii is cle-energized, whereupon switch opens and motor 2l stops. Motor 2l remains fle-energized until the plate voltage reaches point :il at which time the plate current is again suflicient to energize relay le closing' switch 2S thus re--energizing motor El. Wave form [i8 represents the now or electric cu rent to motor 21 and the phase relationship of the motor driving impulse relative to the position of an* tenna i3.

The variable voltage output it of synchro i?. is also applied to a phase-sensitive detector 2i. Waveform 4t represents the sinusoidal output from phase-sensitive detector 2i which is. through a phase shifting network 22. Waveform t in Fig. 2 represents the shifted voltage output of the network 22 which is applied to the grid of the nrst of two stages of overdriven amplincaticn 23. The positive pealrs of wave forni 5e are clipped due to grid current in the overdriven ampli-lier 23.

The plate voltage of the first overdriven ipliier I is represented in Fig. 2 by waveform The plate voltage of the second overdriven ampliner is represented by waveform iii. Reversing relay 24 is the plate load of the second stage of the overdriven amplifiers 23. The broken line running through wave form iii! represents the critical plate voltage, below which the plate current through reversing relay 'it is great enough to energize the relay and throw reversing switch 25 to the position, and above which the plate current through reversing relay 2e is too small to hold the reversing relay 2li energized.. In the latter condition, the reversing switch t5 assumes the second position, reversing the flow of current though field coils 2; of motor 2l; thus reversing the .direction of rotation of motor El. Position 54 on waveform represents the point at which reversing relay 2li becomes energized. rEhe relay 24 remains in this state until position 55 on wave form A52 is reached when it is deenergized and remains in this state 'until position 55 is reached at which time it is again energized. Wave forni 5l in Fig. 2 represents the flow of current in iieid coils 2B of motor 2l with respect to time and position of antenna iii. Thus it is clear from. a study of the phase relationships represented in Fig. 2, that each time the motor cut oil, the reversing relay Eil changes the position ci reversing switch 25 so that the next electric impulse applied to motor 2l reverses the direction of rotation thereof, thus synchronizing the direction of the motor impulse with the direction of rotation of the scanner. From a further study oi the waveforms in Figs. 2, it will be seen that as the gain in voltage amplifier I6 is increased, the slope of the voltage waveforms Al, 52, and lll is increased, thus effectively reducing that part of the cycle during which the motor impulse will he applied to scanner i3, The lower the gain of voltage .ampli-ner l, the smaller is the slope of the voltage waveforms 4 I 42 and 44, thus increasing that part of the cycle during which the motor impulse is applied to scanner I3, thereby giving complete control over the size of sector beine scanned hy the mechanical resonant scanners.

Thus, it is to be clearly understood that the escription and illustration of the invention made above has been given only by way of example and not as a limitation on the scope of the invention, as set forth in the objects and the accompanying claims.

What is claimed is:

i. An electronic control circuit for a mechanical resonant scanner comprising, an alternating current source, means for modulating the alternating current from said source at the oscillating frequency of mechanical resonant scanner. an electric motor, said motor maintaining said mechanical resonant scanner in oscillation, means for controlling the energizing and deenergizing oi motor, and means for reversing said motor for synchronizing the direction .ci rotation of said motor with the Vinstantaneous direction of rotation of said mechanical resonant scanner.

2l. rhe apparatus of claim l in which said means for modulating the alternating current from source at the oscillating frequency of said mechanical resonant scanner comprises, a synchro unit, an element of said synchro unit being mechanically attached to said mechanical resonant scanner, said synchro unit element being so positioned that the voltage output thereo is zero when said mechanically resonant scanner is in a predetermined position, the voltage output f said synchro unit increasing with 4the increase in the angle of rotation of said mechanical resonont scanner.

3. The apparatus of claim l in which said means for controlling the energizing and de-encr giaing ci said motor comprises, an adjustable gain voltage amplifier for ampliiying the mcdue lated voltage output of said modulating means, a detector for, producing a variable voltage from the output of said voltage amplier, a power ampliner and an on-ofi relay, the plate current of said power amplifier being controlled by the output of said detector, said ori-off relay in the plate circuit of said power amplier being energized and deenergized oy the increase land decrease of the plate current of said power amplier, a switch in the electrical circuit of said motor, said switch being closed by said relay when said relay be comes enregized and said switch being opened when said relay becomes cle-energized, said switch thereby controlling the starting and the stopping of said motor, and means for controlling the duty cycle oi said motor comprising an adinstable gain control on said voltage amplier operative when the voltage amplifier gain is in" creased to reduce the duty cycle of said motor and when the amplifier gain is decreased to crease the duty cycle oi said motor.

ll. rEhe apparatus of claim 1 in which said ieans for reversing said motor for synchronizing the direction of rotation of said motor impulse with the instantaneous direction of rotation of said mechanical resonant scanner coinprising a phase sensitive detector, said detector receiving the modulated voltage output of said modulated alternating current source and producing therefrom a substantially sinusoidal voltage wave forni, a phase shifting network for shifting the sinusoidal voltage waveform approximately a quarter cycle in phase, an overdriven amplifier energized by said output of said phase shitting network, and a reversing relay, said overdriven amplifier producing a square wave of output voltage thus controlling the energizing and cle-energizing of said reversing relay, a reversing switch said switch located in the held coil circuit or said motor, said reversing switch being controlled by said reversing relay.

5. An electronic control circuit for a mechanical resonant scanner comprising an alternating current source and a synchro unit, an element of said synchro being mechanically attached to said mechanical resonant scanner, said synchro unit element being so positioned that the voltage output of said synchro unit is zero when said mechanical resonant scanner is in a predetermined position, the voltage output of said synchro unit increasing with the increase in the angle of rotation of said mechanical resonant scanner, whereby the voltage output from said synchro unit is modulated at the oscillatory rate of said mechanical resonant scanner, a voltage amplifier for amplifying the modulated voltage output of said synchro unit, a detector for producing a variable negative voltage from the output of said voltage amplifier, a power amplier and an onof relay, the plate current of said power amplier controlled by the output of said detector, said on-oif relay in the plate circuit of said power ampliiier being energized and (le-energized by the increase and decrease of the plate current of said power amplier, a switch in the electrical circuit of said motor, said switch being closed by said relay when said relay becomes energized and said switch being opened when said relay becomes de-energized, said switch thereby controlling the starting and stopping of said motor, an adjustable gain control on said voltage amplifier, said gain control when increased reducing the duty cycle of said motor and when decreased increasing the duty cycle of said motor, a phase sensitive detector, said detector receiving the modulated voltage output from said synchro unit and producing therefrom a sinusoidal voltage waveform, a phase shifting network for shifting the sinusoidal voltage waveform, approximately a quarter cycle in phase, an overdriven amplifier, and a reversing relay, said overdriven amplifier producing a square wave of voltage when energized by the output of said phase shifting network and controlling the energizing and cle-energizing of said reversing relay, a reversing switch, said switch being in the field coil circuit of said motor, said reversing switch being controlled by said reversing relay, whereby the direction of rotation of said motor is synchronized with the instantaneous direction of rotation of said mechanical resonant scanner.

6. In a control circuit for a mechanical resonant sector scanner having a natural frequency of oscillation, means for generating a signal having an amplitude proportional to the angular displacement of said scanner from the central axis of said sector, motor means connected to said scanner for imparting rotational energy thereto, means for deriving control pulses from said signal for energizing said motor means for a predetermined time interval during each cycle 0f oscillation, said time interval being centered with respect to the time at which said scanner sweeps through the central axis of said sector and means for varying the duration of said time interval whereby the size of said sector is adjusted.

7. In a control system for a mechanical resonant sector scanner having a natural frequency of oscillation, means for producing a signal the amplitude of which is proportional to the angular displacement of said scanner from the symmetrical axis of said sector, a reversible motor coupled to said scanner for supplying rotational energy thereto, means for deriving from said signal first control pulses for energizing said motor for a predetermined time interval during each cycle of oscillation and second control pulses for controlling the direction of rotation of said motor means whereby said motor when energized rotates in a direction corresponding to the direction of oscillation of said scanner whereby said scanner is maintained in continuous oscillation.

8. In a control circuit of the type described in claim 7 wherein means are included for regulating the duration of said iirst control pulses whereby the period of energization of said motor is varied and the size of said sector changed, said first control pulses being centered in time with respect to the time at which said scanner passes through the symmetrical axis of said sector.

9. In a control circuit for a mechanical resonant sector scanner having a natural frequency of oscillation, means for generating a signal the amplitude of which is proportional to the angular deviation of said scanner from the central axis of said sector, motor means coupled to said scanner, means for reversing the direction of rotation of said motor, means for deriving from said signal a first control pulse for operating said reversing means whereby said motor rotates in a direction corresponding to the direction of 0scillation of said scanner and means for controlling the energization of said motor whereby said motor periodically supplies rotational energy to said scanner during an adjustable portion of the cycle centered with respect to the time at which said scanner passes through the central axis of said sector, said last mentioned means determining the size of the sector scanned.

10. In a control circuit as dened in claim 9 wherein said means for generating said signal comprises a synchro unit having rst and second elements, said rlrst element being energized from an alternating current source and being mechanically driven by said resonant scanner whereby a variable amplitude voltage is developed in said second element.

References Cited in the nle of this patent UNITED STATES PATENTS Number Nam-e Date 1,976,935 Gregg Oct. 16, 1934 2,147,674 Satterlee Feb. 2'1, 1939 2,297,719 Satterlee Oct. 6, 1942 2,416,229 Shoemaker Feb. 18, 1947 2,458,175 Kolding Jan. 4, 1949 2,502,975 McFarlane Apr. 4, 1950 

